The present invention relates to an electro-optical device including self-emitting elements, and to an image forming apparatus and an image reader each including the electro-optical device.
Attention has been recently paid to organic light-emitting diode (hereinafter, referred to as OLED) elements, such as organic electroluminescent elements or light-emitting polymer elements, as next-generation light-emitting devices that replaces liquid crystal elements. The OLED elements are self-emitting elements which emit light according to an applied voltage, unlike light valves such as liquid crystal. For example, as disclosed in Japanese Unexamined Patent Application Publication No. 2000-58255 and Japanese Unexamined Patent Application Publication No. 2001-343933, the OLED elements are used in display devices.
Electrophotographic image forming apparatuses in which a line head having a plurality of OLED elements arrayed therein are used as an exposing unit, i.e., a latent image writing unit, have been developed. In addition to the OLED elements, the line head is provided with a plurality of pixel circuits including transistors to drive the OLED elements. For example, Japanese Unexamined Patent Application Publication No. 11-274569 and Japanese Unexamined Patent Application Publication No. 2001-130048 disclose such line heads.
For example, an electro-optical device like the above line head includes a substrate (element substrate) having an area larger than a certain size such that the OLED element are formed. For example, in the techniques disclosed in Japanese Unexamined Patent Application Publication No. 2000-58255 and Japanese Unexamined Patent Application Publication No. 2001-130048, since a circuit element that drives or controls an OLED element is disposed on the element substrate, the element substrate could not keep having an area larger than a certain size. The element substrate is obtained by, first, forming a plurality of OLED elements on one large original substrate, and then dicing the original substrate into a plurality of element substrates. The larger the size of an element substrate corresponding to one electro-optical device is, the fewer the resulting number of element substrates obtained from the original substrate is and the fewer the number of OLED elements obtained from the original substrate is.
Many kinds of materials or many processes are required for forming the OLED elements. Among these processes, there are processes that require cost and time unique to the OLED elements. If a plurality of OLED elements are collectively formed in one original substrate, the resulting manufacturing cost of the element substrates is reduced. Also, the more the number of OLED elements which can be formed on one large original substrate is, the smaller the resulting manufacturing cost of element substrates becomes.